The present invention relates to a semiconductor device fabrication method and fabrication apparatus and, more particularly, to a method and apparatus suitable for nitriding, oxidation, or impurity doping using a plasma.
In a nitriding or oxidation step for surface modification using a plasma or in an impurity doping step using a plasma, the film thickness of a thin film formed on the surface or the impurity amount to be doped is controlled by maintaining the time during which a semiconductor substrate is exposed to the plasma constant.
If, however, the plasma state varies even slightly owing to causes like disturbances, e.g., changes in temperature of a chamber or high-frequency application circuit, changes in flow rate of a gas flow rate controller, or changes in pressure of a pressure controller, the density of a main active species which contributes to a reaction in the plasma changes.
Even in this case, the processing is conventionally performed for a predetermined time. Consequently, the film thickness of a thin film formed on the surface or the impurity amount fluctuates between wafers or lots, and the characteristics of finally formed transistors vary.
The references disclosing techniques concerning the conventional surface modification processes and impurity doping are as follows.
Reference 1: Japanese Patent Laid-Open No. 2002-93781
Reference 2: Japanese Patent Laid-Open No. 2002-231695
Reference 3: Japanese Patent Laid-Open No. 9-205076
Reference 4: Japanese Patent Laid-Open No. 2002-299322